The invention relates to a high-temperature superconductor layer arrangement, comprising at least one substrate and one textured buffer layer, that permits textured growing of a high-temperature superconductor (HTSC) layer.
The buffer layer has a host of different functions. First, it is intended to transfer the texture from the textured substrate, which displays the highest possible degree of texturing, as completely and perfectly as possible to the HTSC layer to be grown. It must be taken into consideration in this context that the substrate is biaxially textured to the greatest possible extent, i.e. both perpendicularly to the layer and in an axial direction within the layer. Corresponding biaxial texturing of the high-temperature superconductor is necessary to achieve high critical currents and high current densities. Furthermore, the buffer layer is intended to prevent any diffusion of constituents or contaminants of the substrate into the HTSC layer, since this can reduce the critical current density and/or the absolute critical current of the high-temperature superconductor, or the superconductive state can be disrupted. Moreover, the buffer layer is intended to display the greatest possible adhesive strength in relation to both the substrate and the high-temperature superconductor to be grown. The buffer layer must additionally display sufficient mechanical and temperature cycling properties, taking both the manufacturing conditions and the operating conditions into account. Furthermore, the buffer layer should permit the simplest possible, reproducible manufacture at a high process speed.
Up to now, a number of different materials have been used as the buffer layer material, such as yttrium-stabilized zirconium oxide (YSZ); various zirconates, such as gadolinium zirconate, lanthanum zirconate and the like; titanates, such as strontium titanate; and simple oxides, such as cerium oxide, magnesium oxide and the like. To fulfill the complex and demanding requirements profile existing today, and particularly to guarantee a high degree of texture transfer and an efficient diffusion barrier, the buffer layer consists of layer combinations comprising multiple, different buffer materials, sometimes five or more layers. The application of multiple layers of buffer material is, however, extremely complex in terms of process engineering, and significantly reduces the production speed of the overall process for manufacturing a functional HTSC layer arrangement, even if continuous processes are used for the manufacture of strips, for example. Use of a single-layer buffer layer made of conventional materials is, however, only inadequately capable of meeting the complex requirements profile.
There is moreover a need to further enhance the quality of the high-temperature superconductor layers in terms of their homogeneity and texture. For example, the proportion of areas of the HTSC layer that do not display HTSC material, e.g. owing to porosity of the HTSC layer or as a result of foreign phases, needs to be minimized as far as possible. Further to be avoided are areas that have incorrect texturing, which can display not only skewing relative to the preferred orientation, but also areas with a completely different crystal orientation. These properties of the HTSC layer can partly be influenced by the choice of the precursors of the HTSC materials in chemical deposition processes, and by the parameters of the deposition and annealing processes, although the effects are difficult to predict and occasionally opposite. Also, because of the multi-component systems of the HTSC materials, the kinetics of the decomposition of the precursors and of the crystallization of the HTSC material are often difficult to control, meaning that changing the process parameters is often undesirable.
As far as possible, these requirements are, in particular, to be met by an HTSC layer arrangement in which the buffer layer and/or the HTSC layer can be manufactured by chemical solution deposition. Owing to the associated processes during thermal formation of the buffer and HTSC layers, special requirements must also be imposed on the production of these layers. In particular, the kinetics of layer formation and crystallization differ fundamentally from the requirements when producing these layers by physical methods, such as pulsed laser deposition (PLD), thermal co-evaporation (TCE), metal-organic chemical vapor deposition (MOCVD), and the like.